Door assembly for an MRI room

Abstract

An MRI room door assembly for use in protecting an entrance to a room containing an MRI scanner system. The assembly comprising a doorframe that is suitable to be fixed in position within or around an opening to the room, a door that is fixed to the doorframe, and an sealing arrangement that seals the door to the frame when it is at rest in the closed position and which is released as a user initiates an opening of the door. At least one or more of the door and the doorframe include a built in safety system which provides a function relating to preventing ferrous objects being brought unintentionally close to the MRI scanner system.

The invention claimed is: 
     
       1. An MRI room door assembly for use in protecting an entrance to a room containing an MRI scanner system, the assembly comprising a doorframe that is suitable of being fixed in position within or around an opening to the room, a door that is fixed to the doorframe, and a sealing arrangement that seals the door to the frame when it is at rest in the closed position and which is released as a user initiates an opening of the door, in which at least one or more of the door and the doorframe include a built in safety system which provides a function relating to preventing ferromagnetic objects being brought unintentionally close to the MRI machine,
 in which the safety system comprises a ferromagnetic detection system (FMDS) arranged in use to warn a person approaching the door with a ferromagnetic object that they should not enter the room through the door with the ferromagnetic object; 
 in which the FMDS comprises: 
 a primary sensor means comprising at least one passive magnetic sensor means which detects the disturbances in the ambient magnetic field which occur as the ferromagnetic object moves through the field; 
 a secondary non-magnetic sensor means which detects movement of objects in the vicinity of the primary sensor means; and 
 a processing circuit which is arranged to monitor the signals from the sensors and to provide an alarm in the event that both the primary and secondary sensor means detect a moving ferromagnetic object, 
 in which the signal processing circuit is configured to identify temporal variations in the measurement signal due to the movement of a ferromagnetic object within the ambient magnetic field and to correlate the identified temporal variations in the measurement signal with instances in which the non-magnetic sensor means detects the presence of an object in its detection zone, and in which the signal processing circuit is arranged to cause the alarm to operate in the event that the correlation is indicative of the presence of a ferromagnetic object in the primary detection zone, and 
 further in which the signal processing circuit is adapted to determine the direction from which the object is approaching the doorway from the output signals from the non-magnetic sensor means and to modify the operation of the alarm dependent on the direction of approach. 
 
     
     
       2. The MRI room door assembly according to  claim 1  in which the safety system is built into the door assembly prior to installation of the door assembly at an MRI room. 
     
     
       3. The MRI room door assembly according to  claim 1  in which the secondary nonmagnetic sensor means comprises a photo-detector which is fitted to the outside of the door assembly, the system also including a light source fitted to the outside of the door assembly and a reflector provided on the inside of the door assembly, the photo-detector receiving a light beam from the source that has passed through the door opening when the door is open and is reflected back onto the photo-detector from the reflector, the FMDS system further comprising a door position determining means which determines when the door has opened sufficiently far to have cleared the light beam. 
     
     
       4. The MRI room door assembly according to  claim 1  in which the FMDS comprises:
 a door position determining means which is adapted to monitor the angular position of the door relative to the entrance, 
 and further comprising a memory which in use stores historical temporal variations in the measurement signal due to movement the ferromagnetic object within the ambient field, and correlation means which is adapted to correlate the stored historical temporal variations in the measurement signal prior to the door moving with incidences in which the non-magnetic sensing means detects the presence of the object in its detection zone, and in which the apparatus is arranged to raise an alarm in the event that the correlation, albeit separated in time, is indicative of the presence of a ferromagnetic object in the vicinity of the magnetic sensor. 
 
     
     
       5. The MRI room door assembly according to  claim 4  which the door position determining means further comprises a user operable release mechanism, such as a door handle, push button, or keypad and a release signal sensor that indicates that a user has operated the release mechanism, in which the FMDS receives the signal from the release mechanism sensor and uses the output from the release signal sensor to determine which historical data to use in the correlation. 
     
     
       6. The MRI room door assembly according to  claim 1  in which the safety system comprises an FMDS comprising:
 a door position determining means which is adapted to monitor the angular position of a door of the entrance, and 
 in which the signal processing circuit is adapted to modify the operation of the alarm in the event that output of the door position determining means indicates that the door is moving. 
 
     
     
       7. The MRI room door assembly according to  claim 1  in which the safety system comprises an FMDS comprising:
 identification means for identifying the person approaching the door, the signal processing circuit being configured to identify temporal variations in the measurement signal due to the movement of the ferromagnetic object within the ambient magnetic field and to correlate the identified temporal variations in the measurement signal with instances in which the non-magnetic sensor means detects the presence of the object in its detection zone, and in which the signal processing circuit is arranged to cause the alarm to operate in the event that the correlation is indicative of the presence of the ferromagnetic object in the primary detection zone but to modify the operation of the alarm according to the identity of the person identified by the identification means. 
 
     
     
       8. The MRI room door assembly according to  claim 1  in which the safety system comprises an FMDS that is operable in a pre-screener mode, the FMDS including means for raising the sensitivity of the primary sensing means when in the pre-screener mode to permit patient screening and lowering it when in the entryway protection mode. 
     
     
       9. The MRI room door assembly according to  claim 8  in which the safety system is arranged so that the pre-screener mode can only be activated with the door closed. 
     
     
       10. The MRI room door assembly according to  claim 1  in which the safety system comprises a barrier which is fixed at one end to the door frame and the other end of which can be moved to a position in which it obscures at least partially the entrance to prevent entrance or egress from the MRI room. 
     
     
       11. The MRI room door assembly according to  claim 10  in which the barrier is an automatic arm, a non-magnetic chain, a curtain or a pair of saloon-door type sprung barriers.